The pageinspect module provides functions that allow you to inspect the contents of database pages at a low level, which is useful for debugging purposes. All of these functions may be used only by superusers.

get_raw_page reads the specified block of the named relation and returns a copy as a bytea value. This allows a single time-consistent copy of the block to be obtained. fork should be 'main' for the main data fork, 'fsm' for the free space map, 'vm' for the visibility map, or 'init' for the initialization fork.

get_raw_page(relname text, blkno int) returns bytea

A shorthand version of get_raw_page, for reading from the main fork. Equivalent to get_raw_page(relname, 'main', blkno)

page_header(page bytea) returns record

page_header shows fields that are common to all PostgreSQL heap and index pages.

A page image obtained with get_raw_page should be passed as argument. For example:

The returned columns correspond to the fields in the PageHeaderData struct. See src/include/storage/bufpage.h for details.

heap_page_items(page bytea) returns setof record

heap_page_items shows all line pointers on a heap page. For those line pointers that are in use, tuple headers are also shown. All tuples are shown, whether or not the tuples were visible to an MVCC snapshot at the time the raw page was copied.

A heap page image obtained with get_raw_page should be passed as argument. For example:

test=# SELECT * FROM heap_page_items(get_raw_page('pg_class', 0));

See src/include/storage/itemid.h and src/include/access/htup_details.h for explanations of the fields returned.

bt_metap(relname text) returns record

bt_metap returns information about a B-tree index's metapage. For example:

fsm_page_contents shows the internal node structure of a FSM page. The output is a multiline string, with one line per node in the binary tree within the page. Only those nodes that are not zero are printed. The so-called "next" pointer, which points to the next slot to be returned from the page, is also printed.

See src/backend/storage/freespace/README for more information on the structure of an FSM page.